Clinicopathologic study of 85 colorectal serrated adenocarcinomas: further insights into the full recognition of a new subset of colorectal carcinoma.

Colorectal serrated adenocarcinoma represents a subtype of colorectal carcinoma that originates from serrated adenomas. Previous studies have suggested a more aggressive course, but this has not been verified. The aim of this work was to test the diagnostic reproducibility of previously proposed histologic criteria for serrated adenocarcinoma and to analyze the clinicopathologic features and outcome that would warrant its recognition as a new subtype of colorectal cancer. Nine hundred twenty-seven consecutive colorectal cancer specimens were used to search for cases fulfilling the criteria of serrated adenocarcinoma and matched controls. Clinicopathologic findings of 85 serrated adenocarcinomas were compared with a matched control group of conventional cancers. Serrated adenocarcinomas were encountered in 9.1% (n = 85) of cases. Residual serrated adenoma was present in 44 (51.7%). Absence of residual adenoma did not have any influence on the parameters studied. Interobserver variation between 2 Spanish and a Finnish pathologist showed moderate agreement (κ = .5873). Compared with their matched controls, serrated adenocarcinomas were more often accompanied by synchronous residual serrated adenomas (P < .0001), remote serrated adenomas (P = .0035), and serrated adenocarcinomas or cancers representing partial features of these tumors (P = .002). They had a less favorable 5-year survival than conventional cancers (P = .048 Breslow, Kaplan-Meier), and left-sided ones had the worst prognosis (P = .001). Serrated adenocarcinoma is an identifiable subset of colorectal cancer; and the histopathologic differences, in addition to its less favorable prognosis, may justify its recognition as a distinct subset of colorectal cancer warranting the search for specific clinical management strategies.